Sheet binding methods using toner as glue or adhesive for bonding together multiple sheets of recording media are known. For example, in JP-H07-223387-A, toner is softened with heat and is used as adhesive for binding documents, thereby obviating the need for disposable binding elements, such as staples or clips that are discarded when the documents bound thereby are discarded. Specifically, adhesive toner is applied to a binding margin of a sheet, and a binding margin of another sheet is superposed thereon. Then, the binding margins of the sheets are heated and pressed, thereby binding together the sheets.
JP-2000-255881-A also proposes a sheet binding device using adhesive toner to attain high-quality sheet binding in reduced processing time and to obviate the need for adjusting fixing conditions such as heating time or pressing time in accordance with changes in binding-related variables such as the number of sheets to be bound together. Specifically, in JP-2000-255881-A, in addition to a fixing device for fixing images according to image data, another fixing member is provided to fix adhesive toner applied to the binding margin each time the sheet is superimposed on the sheet stacked on a discharge tray, thereby binding together the sheets.
Additionally, in binding multiple sheets together, it is preferable that binding strength, that is, the strength of bonding by toner adhesion, is adjustable in accordance with increases in the number or thickness of sheets bound together.
In the case of metal staples, although binding strength may be adjusted with the size, strength, or hardness of the metal staple in accordance with the number of stacked sheets, large or hard staples cannot be removed from sheets easily. It is possible that sheets are damaged when the staples are being removed thereof.
Additionally, in binding sheets with staples, it is inevitable that binding strength is constant throughout the sheets bound together.
Additionally, in bonding sheets with adhesive toner, it is necessary to determine layout of the binging margin (hereinafter also “bonding range”) to which adhesive toner is applied so that adhesive toner does not adversely affect an image according to image data.